I don't know what pruning schedule my clematis are on

[QuiteUnbelievable]

What shall I do ?

Do you know what the flowers look like and remember what time of year they flowered last year?
Then you should be able to work it out by finding which variety they are?

Do you know if they flower in Spring or later on in the summer?

Some flower all summer and some seem to shine in may and June sometimes another flush later ln

As a general rule, don't prune anything (clematis or otherwise) that is about to flower!
I think you may be too late for the May-flowering ones (Group 2); the prune should have been done in February. But you can do a deadhead, back to a growth bud, after the first flush.
Late summer (Group 3) also wanted a February prune.

I have a Clematis Jackmani plant , very new , bought it recently as a tiny green plant , it is going great guns , about 34" tall now but very spindly .
It's on the windowsill in the kitchen until I can trust the temperatures .

Should I pinch the top out or let it keep going ?